add download api

index.js

@@ -784,6 +784,10 @@ class HyperDB {
     if (this.updates.size > 0) await this._flush()
     if (this.autoClose === true) await this.close()
   }
+
+  download() {
+    return this.engine.download()
+  }
 }
 
 function maybeClosed(db) {

lib/engine/bee.js

@@ -170,6 +170,9 @@ module.exports = class BeeEngine {
     await batch.flush()
   }
 
+  // dummy cause we are phasing bee1 out
+  async download() {}
+
   clearRequests(reqs) {
     Hypercore.destroyRequests(reqs, null)
   }

lib/engine/bee2.js

@@ -202,6 +202,10 @@ module.exports = class Bee2Engine {
     await batch.flush()
   }
 
+  download() {
+    return this.db.download()
+  }
+
   clearRequests(reqs) {
     Hypercore.destroyRequests(reqs, null)
   }

lib/engine/rocks.js

@@ -178,6 +178,10 @@ module.exports = class RocksEngine {
     await this.write.flush()
   }
 
+  download() {
+    // api parity
+  }
+
   clearRequests(reqs) {
     // api parity
   }

test/replicate.js

@@ -192,3 +192,54 @@ test('requests are cleared on close from unclosed snap', async function ({ creat
     await clone.close()
   })
 })
+
+test(
+  'download makes the db readable offline',
+  { rocks: false, bee: false },
+  async function ({ create }, t) {
+    const db = await create()
+
+    const tx = db.transaction()
+    for (let i = 0; i < 100; i++) {
+      await tx.insert('@db/members', { id: 'member-' + i, age: 20 + (i % 50) })
+    }
+    await tx.flush()
+
+    const expected = await db.find('@db/members').toArray()
+    t.is(expected.length, 100)
+
+    const clone = await create({ key: db.core.key, autoUpdate: true })
+
+    const unreplicate = replicate(t, clone, db)
+
+    await new Promise((resolve) => clone.core.once('append', resolve))
+
+    await clone.download()
+    await unreplicate()
+
+    // every read must be served locally now, no peers connected
+    const members = await clone.find('@db/members').toArray()
+    t.alike(members, expected)
+
+    const one = await clone.get('@db/members', { id: 'member-42' })
+    t.alike(one, { id: 'member-42', age: 62 })
+
+    const range = await clone.find('@db/members', { gte: { id: 'member-9' } }).toArray()
+    t.is(range.length, 11)
+
+    await clone.close()
+    await db.close()
+  }
+)
+
+test('download is a no-op on engines without it', { bee2: false }, async function ({ create }, t) {
+  const db = await create()
+  await db.insert('@db/members', { id: 'someone', age: 40 })
+  await db.flush()
+
+  await db.download()
+
+  t.alike(await db.get('@db/members', { id: 'someone' }), { id: 'someone', age: 40 })
+
+  await db.close()
+})